(a) Field of the Invention
The present invention relates to a photosensitive material for use in electrophotography, in particular a laminate-type electrophotographic photosensitive material capable of obtaining a dichromatic (two colors, such as black and red) reproduction from a multi-color original through only one exposure process, as well as the usual monochromatic reproduction.
(b) Description of the Prior Art
As typical photosensitive materials for use in conventional Carlson process (photosensitive materials for use in electrophotography) there are well known photosensitive materials comprising a selenium photoconductive layer on a conductive substrate, a charge transfer layer made of polyvinyl carbazole or the like on said selenium photoconductive layer, and so forth.
These photosensitive materials are devised so that the surface potential thereof may hold a single positive or negative polarity in compliance with an electrostatic latent image to be formed through electrification-exposure processes. In order to obtain dichromatic reproductions using such photosensitive materials, therefore, it is ordinarily required to repeat the cycle of electrification-exposure-development-transfer. However, by the mere repetition of this cycle there can not be obtained a distinct dichromatic image owing to the occurrence of mixed colors, fog, shear in position, etc.
Reflecting this actual condition, there has been proposed a process of obtaining a dichromatic copy (Japanese Open Patent Application No. 144737/1978) which comprises the steps of carrying out a first corona electrification of a photosensitive material prepared by forming an insulating layer and a photoconductive layer, in that order, on a conductive substrate, performing the overall radiation of the thus electrified material with a light belonging to the sensitive region of said photoconductive layer either simultaneously with or after the first corona electrification, carrying out a second corona electrification of this material with a polarity opposite to that in the first electrification simultaneously with the imagewise exposure of the original having white, black and red areas (namely, the dichromatic original with red and black image areas) through a red complementary color filter, and performing the imagewise exposure again through a red filter, whereby there is created in the material wherein a condition the charged polarity of the electrostatic latent images formed on the red and black areas corresponding to the original has become opposite. Thereafter, these latent images are successively developed with toners of opposite polarity and different colors, and the resulting toner images are transferred onto image-receiving papers such as paper and are fixed thereon. However, this process is still defective in that considerably large quantities of exposure light are required in addition to the trouble of utilizing different filters two times.